Production of divinylated aromatic hydrocarbons



Patented Au 13, 1940 PRODUCTION OF 2,211,524 nrvnwm'ran AROMATIC HYDROCARBONS Herbert Muggleton Stanley, Tadworth, Gregoire Minkofl, Epsom, and James Ernest Youell.

Waliington, England No Drawing. Application October 15, 1937, Se-

rial No. 169.332. In Great Britain October 3 Claims.

This invention relates to the production of aryl substituted oleflnes by condensation of aromatic hydrocarbons with unsaturated aliphatic hydrocarbons containing from 3 to 5 carbon atoms, and subsequent pyrolysis of the condensation-products.

as benzene may be condensed with unsaturated aliphatic hydrocarbons by Friedel and Crafts reaction employing aluminium chloride as condensing agent and it has been proposed to use strong sulphuric acid for the purpose. A particularly advantageous method of production using strong sulphuric acid is described and claimed in the specification of our patent application No. 169,330 of even date. As explained in the aforesaid specification the process can be regulated to favour the production of a di-alkylated aromatic hydrocarbon, e. g. p-di-isopropylbenzene, as compared w.th the production of the mono-alkylated product. A suitable ratio of propylene to benzene for p-di-isopropyl benzene production is 1 to 1.

Having obtained the di-alkylate'cl alromatic hydrocarbon either by known methods or by the method of using concentrated sulphuric acid under the conditions specified in the aforesaid patent application of even date the present invention is concerned with certain novel features of conversion of the same by pyrolysis into the corresponding di-vinyl body and its utilisation in producing certain useful resins.

We have found that pyrolysis generally produces relatively large proportions of undesired substances the formation of which can be minimised, so far as we have been able to ascertain, only by observing certain operating conditions the chief of which are the following:

(1) Using an operating temperature lying between 600 and 800 C. preferably between 650 and 750 C., the hydrocarbon being thereby pyrolysed in the gaseous phase.

(2) Ensuring a linear gas velocity along the reaction zone in excess of the critical velocity, i. e. a velocity several times the critical velocity so as to ensure turbulence. Unless such a high velocity is maintained not only is the yield of desired products very low, but the reaction tube speedily becomes choked and renders continuous operation impossible.

(3) Controlling the character of the products of pyrolysis by adding to the main reactant one or more of the products of thermal dehydrogenation as will now be explained by reference to the pyrolysis of p-di-isopropylbenzene. The pyrolysis It is known that aromatic hydrocarbons such I according to the present invention is preferably carried out at about atmospheric pressure or at sub-atmospheric pressure. mospheric pressures'are not precluded,for example up to say 5 atmospheres.

The controlled pyrolysis of p-di-isopropylbenzene at temperatures of 600-800 C. is represented by the equations:

The'same considerations apply to other bodies of the same class, that is to say divinylated aro- Moderate super-at- I matic hydrocarbons of the type of divinyl benzene or its di-methyl derivatives can be obtained by condensation of propylene or its homologues with benezene or its homologues followed by pyrolysis of the condensation product. Such divinylated aromatic hydrocarbons are of value in the production of resins from styrene hydrocarbons by polymerisation. In fact, the properties of resins formed by polymerisation of styrene hydrocarbons is, as is well known, favourably influenced in certain directions .by the presence of divinylated aromatic hydrocarbons of the type of divinylbenzene. For instance it is known that polymerisation of styrenes in the presence of certain divinylated hydrocarbons leads to the formation of resins insoluble in organic solvents.

The divinylated aromatic hydrocarbon e. g., divinyl benzene may be produced of itself and then be added to the styrene hydrocarbon or a solution thereof, whereupon the mixture is polymerised, but it is possible to start with a mixture of mono-alkylated and dialkylated aromatic hydrocarbons e. g., mono-isopropylbenzene and p-diisopropyl benzene in selected proportions and to pyrolyse the same so as to produce a mixture of styrene and divinyl benzene in pre-desired proportions and then proceed to polymerise the mixture.

In general both dehydrogenation and demethanation products are present in the products of cracking as well as substantial proportions of substances such as p-isopropylstyrene, in which only one isopropyl residue has undergone thermal rupture. The fact that a mixture of reaction proddots is always obtained does not militate against the value of the process since it has been found that such a mixture (first freed from heavy tars by vacuum distillation) may be employed directly without preliminary separation, to influence in a highly favourable manner the course of the polymerisation of styrene and its simple homologues. Nevertheless, in order to obtain the highest concentrations of divinylated substances, the cracking must be efiected in such a way that relatively high percentage decomposition per pass are obtained, 1. e. that 70% or over of the di-isopropylbenzene undergoes reaction in a single passage. This necessitates the employment of high linear gas velocities and also, preferably, the use of gaseous diluents, particularly steam and hydrogen.

The pyrolysis may be effected at 600 to 800 C. in tubes of silica, copper, steel and especially Follsained steel at linear gas velocities substantially above .the initial velocity e. g. ft./sec. in a V bore tube, with steam or hydrogen (or both) as diluents, and percentage decompositions per passage should preferably be over and may exceed without appreciable carbon formation. The yield of divinylated hydrocarbons such as divinyl benzene is further improved by fractionating the products of cracking and returning the fraction of the products rich in p-isopropylstyrene and unchanged p-di-isopropylbenzene to the cracking process.

Example 1 A mixture of vapourised di-isopropylbenzene and 4 molecular proportions of hydrogen was passedat a feed rate of about g./hr. of hydrocarbon through a long copper tube of 7 mm. bore having an effective cracking zone-of about 75 cc., and heated to a temperature of about 675 C. The hydrocarbon products, amounting to 89% by weight of the weight of hydrocarbon Example 2 A pre-heated mixture of di-isopropylbenzene vapour and 3 molecular proportions of steam was passed at a speed of about 120 grams/hr. of hydrocarbon through a Follsained steel tube of /4 inch bore heated over about 25" of its length to approximately 675 C. The condensed liquid products amounting to about 88% of the hydrocarbon feed were fractionated under reduced pressure to yield the following fractions:

(I) B. P. up to 83.5? C./12 mm "48% of total (II) B. P. 83.5/l2 mm.-87.0 C./ 12

mm l7% of total (III) B. P. 87.0 C./ 12 mm.-l02 C./ 12

mm. 25% of total (IV) Residue 10% of total Fraction I containing substantial proportions of mono-olefine and some unchanged di-isopropylbenzene can be further cracked to yield more divinylated products. Fractions II and 111 had bromine addition values (McIlhiney) of 85 and respectively and contained large proportions of divinylated hydrocarbons as shown by the formation of insoluble polymers on thermal polymerisation. The addition of as little as 0.01% of fraction III to a pure monomeric styrene caused the formation of insoluble polystyrene resins when the mixture was thermally polymerised at C. for 40 hours.

What we claim is:

1. The method of producing divinyl aromatic hydrocarbons which comprises subjecting a di- (a-alkyl-ethyl)-benzene in which the a-alkyl group contains from 1 to 3 carbon atoms, to pyrolysis whereby hydrogen and a di-(a-alkylvinyD-benzene, in which the a-alkyl group contains from 1 to 3 carbon atoms, are formed in a side reaction as undesirable dehydrogenation products, and controlling the said side reaction by the addition to the material undergoing pyrolysis of at least one of the said dehydrogenation products in an amount suflicient to suppress said side reaction.

2. The method of producing divinyl aromatic hydrocarbons which comprises subjecting a di- (a-alkyl-ethyl) -benzene in which the a-allwl group contains from 1 to 3 carbon atoms, to pyrolysis whereby hydrogen and a di-(a-alkylvinyl) -benzene, in which the a-alkyl group contains from 1 to 3 carbon atoms, are formed in a side reaction as undesirable dehydrogenation products, and controlling the said side reaction by the addition to the material undergoing pyrolysis of hydrogen in an amount sufiicient to suppress said side reaction, the pyrolysis being effected at a temperature between 600 C. and 800 C. at a high linear gas velocity equivalent to at least a gas velocity of 50 feet per second in a inch bore pyrolysis tube.

- 3. The method of producing divinyl aromatic hydrocarbons which comprises subjecting a di- (a-alkyl-ethyD-benzene in which the a-alkyl group contains from 1 to 3 carbon atoms, to pyrolysis whereby hydrogen and a di-(w-alkylvinyD-benzene, in which the a-alkyl group contains from 1 to 3 carbon atoms, are formed in a side reaction as undesirable dehydrogenation products, and controlling the said side recation by the addition to the material undergoing pyrolysis, of a di-(a-alkyl-vinyD-benzene, in which the a-alkyl group contains from 1 to 3 carbon atoms in an amount suflicient to suppress said side reaction, the pyrolysis being effected at a temperature between 600 C.and 800 C. at a high linear gas velocity equivalent to at least a gas velocity of 50 feet per second in a inch bore pyrolysis tube.

HERBERT MUGGLETON STANLEY.

GREGOIRE MINKOFF.

JAMES ERNEST YOUELL. 

